理论探究水溶液条件对TMN_(x)C_(y)催化氮还原性能的增强机制

Theoretical Research on Catalytic Performance of TMN_(x)C_(y) Catalyst for Nitrogen Reduction in Actual Water Solvent

在电化学氮还原(NRR)合成氨过程中,为了认识真实水环境对过渡金属掺杂氮碳材料催化NRR活性的影响,并筛选出实际催化性能最佳的构型,本研究通过密度泛函理论(DFT)和从头算分子动力学(AIMD)相结合的方法,对一系列不同配位形式的过渡金属掺杂氮碳催化剂(TMN_(x)C_(y), TM=Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn;x=1~4;y=4-x,总共40种构型)催化NRR的热力学稳定性和实际氮还原催化活性进行了系统研究.计算结果表明,本工作所研究的40种催化剂结构均具有较高的热力学稳定性,可作为实际的NRR候选催化剂.其中,利用隐性+显性水溶剂模拟真实水环境时,过渡金属V掺杂形成的VN3C1结构催化NRR酶机制过程的最大吉布斯自由能变值仅为0.35eV(在U=0 V vs. RHE时),表现出最佳的NRR催化性能.总体而言,本研究采用DFT与AIMD相结合的方法,深入地阐述了TMN_(x)C_(y)催化剂的实际NRR催化过程,为实验过程做出了更为贴切的理论预测.

Currently, the electrocatalytic nitrogen reduction reaction(NRR) is a significant catalytic process under ambient conditions. For the N_(2) fixation reaction, the metal-based catalysts are the most widely explored catalysts, but compared to the traditional Haber-Bosch process, the poor resistance and low selectivity to acids or bases, and the low Faradaic efficiency, production rate, and stability of metal-based catalysts, make them uncompetitive with industrial N)(2) fixation. During these years, inspired by applications of carbon material catalysts for electrocatalytic field, the carbon material catalysts have attracted great attention, especially for transition-metal-doped carbon material catalysts. In this work, to obtain insight into the influence of water ambient condition on the catalytic performance of transition-metal-doped carbon material catalyst for electrochemical NRR, and to screen out the optimal catalyst structure with excellent catalytic performance, herein, under actual ambient conditions, we systematically described the thermodynamic stability and catalytic performance of a series of transition-metal-doped carbon material catalysts(TMN_(x)C_(y), TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, x=1~4, y=4-x, 40 models) for NRR by means of density functional theory(DFT) and ab initio molecular dynamics(AIMD) simulations. To simulate water condition during the NRR, we employed a mixed implicit+explicit solvation model, in which explicit water molecules are included in the first solvation shell, forming hydrogen bonds with the intermediate adsorbates of NRR, and an implicit solvent model captured longer-range solvation effects. The calculation results indicate that the 40 catalysts possess high thermodynamic stability, even at 700 K, and can be used as potential catalysts toward ammonia synthesis. It is noted that VN_(3)C_(1) catalyst exhibits the best performance via a NRR enzymatic pathway under the actual water ambient condition with a mixed implicit+explicit solvation model, which has a lowest change value of free energy of 0.35 eV(at U=0 V vs. RHE) for potential-determining step. These results may reveal a new perspective for artificial ammonia synthesis using a single-atom catalyst under actual ambient conditions.